This invention relates generally to vehicle brakes, and particularly to an improved automatic brake shoe clearance adjusting device for shoe drum type brakes.
One of the conventional automatic brake shoe clearance adjusting devices comprises a first strut member with a fork-shaped portion on one end and threaded stem portion on the other end, a second strut member having a hollow end portion for loosely receiving the threaded stem portion of the first strut member, and an adjusting nut screw-threadingly engaging with the threaded stem and abutting with the open end of the hollow end portion of the second strut member and having ratchet teeth on the outer circumference. An adjusting lever having a pawl portion cooperating with the ratchet teeth is pivotally mounted on a hand brake lever, and a bent portion of the adjusting lever is normally biassed against a shoulder of the hand brake lever acting as a stop by means of a spring extending between the hand brake lever and the adjusting lever. The adjusting lever is mounted on a pin secured to the hand brake lever with some amount of play or degree of freedom of movement in the direction of the thickness of the hand brake lever or the direction of the axis of the pin so that the pawl portion of the adjusting lever can move towards or away from the ratchet teeth of the adjusting nut. However, the bent portion of the adjusting lever can also move in the direction of the thickness of the hand brake lever due to the play aforementioned, and thus there is a tendency for the adjusting lever to disengage from the stop of the hand brake lever due to vibrations of the vehicle in usage or due to mishandling of a tool in assembling the brake. It is possible to overcome such drawbacks by reducing the amount of play, but the movement of the adjusting lever in passing over the ratchet teeth will accordingly be restricted, and the adjusting nut may be rotated in the reverse direction upon releasing the hand brake lever.